Two xylan-containing lignocellulosic raw materials (rice husks and Eucalyptus globulus wood) were subjected to autohydrolysis under optimised conditions, yielding liquors containing soluble xylan-degradation products and a solid phase enriched in cellulose. Autohydrolysis liquors were acidified with sulfuric acid and heated to yield xylose-containing solutions suitable for the fermentative production of lactic acid, which can be easily converted into polylactic acid (PLA). The solids from autohydrolysis treatments were dried and mixed with PLA (in relative weight proportions 30:70) to give biodegradable composites. The mechanical properties of composites were assessed by tensile and impact tests. Microscopic analysis revealed that the particles of autohydrolysed lignocellulosics were evenly distributed in the PLA matrix. The interfacial compatibility between PLA and reinforcing agents was assessed by scanning electron microscopy.